/Engine/Source/Runtime/Slate/Public/Framework/Application/SlateApplication.h
an array of top-level windows that can be interacted with. e.g. when a modal window is up, only return the modal window
[TArray](API\Runtime\Core\Containers\TArray)< [TSharedRef](API\Runtime\Core\Templates\TSharedRef)< [SWindow](API\Runtime\SlateCore\Widgets\SWindow) > > GetInteractiveTopLevelWindows()